v. & n.
v.intr. (usu. foll. by into) fall back or sink again (into a worse state after an improvement).
n. also the act or an instance of relapsing, esp. a deterioration in a patient's condition after a partial recovery. relapsing fever a bacterial infectious disease with recurrent periods of fever. relapser n.
[ L relabi relaps- (as RE-, labi slip) ]